Automobile interior trim is often engineered to minimize wall thickness, while maintaining desired structural characteristics. Greater wall thickness of such molded articles requires more raw material per unit part, thereby undesirably increasing the cost of production and increasing vehicle weight. Furthermore, greater wall thicknesses slow down production time due to longer cycling periods needed to permit cooling of thicker molded regions.
Automotive trim components or articles, such as interior panels are often molded from thermoplastic to have various protrusions extending from a broad panel surface, which protrusions serve different functions. For example, some trim components are provided with stiffening ribs to reduce twisting or flexing of the part. The same or other trim components may be provided with fastening bosses that add rigidity and/or strength to areas of the part that are to be secured or fastened to another structure. For example, a screw receiving hole in a molded article may be surrounded by an annular protrusion for support. Such annular protrusion may also have radially outwardly extending protrusions (as an asterisk) to provide further support. As another example, standoffs may be formed on the broad surface of the part to provide proper spacing from an abutting component. As a further example, a protrusion may be in the form of a dog house or cage, which is used to secure the article or trim component to some other part, e.g., by a hook.
Because it is desirable to manufacture automotive parts with the least amount of material as possible, without sacrificing performance, it is desirable to make the types of protrusions mentioned above as small as possible, so long as they achieve their intended function. Oftentimes, it is desirable to make the protrusions with a thickness of 1/10″ or less (i.e., measured in a direction parallel to the surface from which the protrusion protrudes and perpendicular to the longitudinal direction of the protrusion).
It can be appreciated that protrusions of such narrow cross section may be subject to chipping or breakage. As the protrusion protrudes further from the base surface, it becomes more prone to breakage. In addition, several of such protrusions are of a tapered configuration terminating in a relatively narrow pointed tip. Such tip is often less than 1/10″ thick and is highly prone to chipping.
Of course, almost all thermoplastic automotive trim components are reinforced by reinforcement materials. More specifically, it is known to use glass fibers to reinforce thermoplastic trim components. Such glass fibers typically have a length on the order of about ⅛″. When glass-reinforced thermoplastic materials are molded in high pressure injection molding operations (e.g., of pressure levels greater than 15,000 PSI), movement of the molten material, for example, through a gate and runner system, causes the glass fibers to align themselves longitudinally with the longitudinal or longer extent of the projection. In this manner, even though the glass fibers have a length greater than the thickness of the protrusions, the thickness or width of the aligned fibers (typically about 6–20 microns) will fit into the protrusions to reinforce the protrusions adequately.
However, for certain applications, it is desirable to mold the thermoplastic articles in a low pressure compression molding method (e.g., less than 3,000 PSI). In such method, molten thermoplastic is introduced into a cavity. The mold is then closed, and excess material is squeezed between the die surfaces so that the molten material fills all gaps and shapes to form the part. The part can thus be finished in a one-step process.
One drawback with the conventional low pressure compression molding methods, however, is that where a pan is to be highly reinforced, e.g., requiring 25–35% by volume glass fibers, the glass reinforcement fibers inhibit substantial flow of molten material. As a result, the fibers do not align with the longitudinal direction of the protrusions, and an insufficient amount of glass fibers will enter into protrusions of thicknesses of 1/10″ or less. Thus, these protrusions would need to be made thicker, or otherwise not be reinforced to the extent desirable.
It is an object of the invention to provide a highly reinforced molded part that can be provided with equally reinforced protrusions of a thickness less than 0.1″. In order to achieve this object and to overcome the problems noted above, the present invention provides a reinforced molded article comprising a main portion which has opposing major surfaces defining a thickness of the main portion. A protrusion is integrally molded with the main portion and protrudes from one of the surfaces, the protrusion having a thickness of less than the thickness of the main portion and less than about 0.1″. The protrusion has a height of at least twice the thickness of the protrusion. The main portion and the protrusion are formed from a material comprising at least one thermoplastic, and about 2% to about 15%, by volume, of reinforcing particles. The particles each comprise one or more layers, wherein at least 50% of the reinforcing particles are less than about 20 layers thick, at least 99% of the reinforcing particles are less than about 30 layers thick, and the layers comprise platelets having a thickness of between about 0.7 nm and 1.2 nm.
It is a further object of the invention to provide a method of manufacturing a highly reinforced molded part that has the equally reinforced protrusions as discussed above. In accordance with this object, the present invention provides a method of producing a reinforced article comprised of a main portion which has opposing major surfaces defining a thickness of the main portion. A protrusion is integrally molded with the main portion and protrudes from one of the surfaces, the protrusion having a thickness of less than the thickness of the main portion and less than about 0.1″. The protrusion has a height of at least twice the thickness of the protrusion. The method prepares a melt of at least one thermoplastic, and about 2% to about 15%, by volume, of reinforcing particles. The particles each comprise one or more layers. At least 50% of the reinforcing particles are less than about 20 layers thick, at least 99% of the reinforcing particles are less than about 30 layers thick, and the layers comprise platelets having a thickness of between about 0.7 nm and 1.2 nm. The melt is compressed between die surfaces at a pressure of less than 3,000 PSI, the die surfaces having recesses corresponding to the shape of the protrusions and receiving the melt, including the 2%–15% by volume reinforcing particles, in the recesses so that the melt conforms to the shape of the recesses. The melt is cooled, and the cooled portions of the melt that are received in the recesses form the reinforced protrusions.
These and other objects of the invention can be more fully appreciated from the following detailed description of the preferred embodiments.